Embodiments relate to air handling units and, more particularly, to methods and systems for active sound attenuation in an air handling unit.
Air-handling systems (also referred to as air handlers) have traditionally been used to condition buildings or rooms (hereinafter referred to as “structures”). An air-handling system may contain various components such as cooling coils, heating coils, filters, humidifiers, fans, sound attenuators, controls, and other devices functioning to at least meet a specified air capacity which may represent all or only a portion of a total air handling requirement of the structure. The air-handling system may be manufactured in a factory and brought to the structure to be installed or it may be built on site using the appropriate devices to meet the specified air capacity. The air-handling compartment of the air-handling system includes the fan inlet cone and the discharge plenum. Within the air-handling compartment is situated the fan unit including an inlet cone, a fan, a motor, fan frame, and any appurtenance associated with the function of the fan (e.g. dampers, controls, settling means, and associated cabinetry). The fan includes a fan wheel having at least one blade. The fan wheel has a fan wheel diameter that is measured from one side of the outer periphery of the fan wheel to the opposite side of the outer periphery of the fan wheel. The dimensions of the air handling compartment such as height, width, and airway length are determined by consulting fan manufacturers data for the type of fan selected.
During operation, each fan unit produces sounds at frequencies. In particular, smaller fan units typically emit sound power at higher audible frequencies, whereas larger fan units emit more sound power at lower audible frequencies. Devices have been proposed in the past that afford passive sound attenuation such as with acoustic tiles or sound barriers that block or reduce noise transmission. The acoustic tiles include a soft surface that deadens reflected sound waves and reverberation of the fan unit.
However, passive sound attenuation devices generally affect noise transmission in certain directions relative to the direction of air flow.
A need remains for improved systems and methods to provide sound attenuation in air handling systems.